This chapter represents an overview of nanosensors as novel detection and monitoring tools for environmental pollutants. Environmental contamination has risen every day due to industrial activities, urbanization, and agricultural practices, and the sensitivity, specificity, and real-time observation needs have risen enormously. Consequently, the nanosensors using the nanomaterials such as carbon nanotubes, graphene and metal oxide over the conventional sensing technology and advantage of high surface area and electrical properties; they permit low concentration pollution detection. These nanosensors can effectively detect a range of contaminants in the air and water, including heavy metals, volatile organic compounds, and pathogens. By integrating with advanced data processing technologies like the Internet of Things (IoT), they allow for real-time data transmission and analysis, which supports prompt responses to pollution incidents. However, despite their promising capabilities, the use of nanosensors encounters several challenges, including inconsistencies in sensor performance, selectivity, stability issues, and regulatory concerns surrounding the safety of nanomaterials.In addition to the transformational use of nanosensors in enhancing our understanding of environmental pollutants, work in this field serves to highlight further the continuing need for research and development to help overcome present and future challenges. Nanosensors could play a decisive role in the quest for sustainable health protection for the public and the environment by providing actionable information that illuminates dynamics about pollution and performs efficient remediation approaches. This chapter involves the basic principles, classification and various applications of nanosensors in environmental monitoring. We delve into the advantage of the use of nanosensors: high sensitivity, high selectivity, and portability.